when i first got my urban express, it had the stock belt that was so worn down it was fitting way down in the pulley, and it predictably had pretty good take off. only 28mph topend, but I would call it "peppy." I have been pretty happy with the people's pipe . i briefly ran it with the stock belt, lighter weights, this pipe, and stock jetting. pretty decent off the line for a completely stock cylinder.
the bx31 gives you that top SPEED but considerable low end power loss